NOTE – Loss relative to free space may be divided into losses of different types, such as:

- absorption loss, for example by ionospheric, atmospheric gases or hydrometeors;
- diffraction loss, as for ground waves;
- effective reflection or scattering loss as in the ionospheric case including the results of any ionospheric focussing or defocussing;
- polarization coupling loss, which can arise from any polarization mismatch between the antennas for the particular ray path considered;
- antenna gain degradation, as in tropospheric scatter propagation;
- losses due to phase interference between the direct ray and rays reflected from the ground, other obstacles or atmospheric layers.